1. Field of the Invention
The invention is in the field of joined cast ductile iron pipe. More specifically, it is in the field of joining ductile iron pipe in such a manner that they will not separate when subjected to axial loads as well as other loads associated with buried pipe lines.
2. Description of the Prior art
It is common practice to make pipe joints wherein one pipe having a spigot or plain end is pushed into the bell end of another pipe. To prevent leakage a soft rubber ring with a hard rubber insert on one side is placed into the bell of the outside pipe, prior to the insertion of the plain end.
To prevent the pipes from separating under pressure such joints have been modified by using radially extending locking segments inserted in the bell of a first pipe and engaging a circumferential weldment on the outside of a second pipe telescoped inside the first pipe.
Such a method is described in U.S. Pat. No. 4,540,204. This patent represents the most recent prior art known to the inventors. However, when applying the prior art method to very large pipe, e.g., those 42 inches and larger, the method exhibits a need for improvement. Such need is most apparent in a deflected joint when a pipe with a bell opening having the maximum tolerance permitted is joined with a pipe having a plain end whose diameter is the minimum permitted. In such cases, the locking segment can become misaligned with the barrel of the inner pipe. This misalignment of the locking segments in a pressurized pipe line can allow the weldment on the inner pipe to move under the locking segment either partially or completely. In the first instance, preventing disassembly while in the second and more important, allowing the two pipe to become disengaged, i.e., failure of the joint. While failure of the prior art joint at normal working pressures should not be anticipated, it is possible to achieve higher working pressures with the improved locking segment of the present invention.